In recent years, development of ferroelectric memory (FeRAM: ferroelectric random access memory), which retains information in a ferroelectric capacitor structure using polarization inversion of a ferroelectric, is in progress. Ferroelectric memory is a non-volatile memory in which the retained information does not disappear when power is turned off, and is attracting attention particularly because realization of high integration, high-speed drive, high durability, and low power consumption can be expected with it.
The structure of a capacitor used for a memory cell of FeRAM has a structure in which, as described in Patent Documents 1 to 3 which will be described below, an SBT film or a PZT film for example is used as a ferroelectric film, and the ferroelectric film is sandwiched by a lower electrode and an upper electrode. A platinum film for example is used as the lower electrode, and a platinum film, an iridium oxide film, or the like for example is used as the upper electrode.
Patent Document 1 discloses an approach which, for suppressing separation and mutual diffusion of constituting elements of the ferroelectric film, does not perform high-temperature thermal treatment between the step of crystallizing the ferroelectric film completely to the step of forming a protection film of the capacitor structure. Specifically, PZT, which is a ferroelectric, is used first as a material to form a capacitor film, and thereafter this film is crystallized by RTA (Rapid Thermal Annealing) method. Subsequently, IrOx (0<x<2) is used as a material to form the upper electrode, and RTA method is further performed to crystallize the capacitor film completely. Simultaneously, iridium (Ir) in the upper electrode is made to diffuse into the PZT. According to this approach, it is possible to prevent the mutual diffusion between the electrodes and the ferroelectric film as well as separation of the constituting elements of the ferroelectric film.
Patent Document 2 discloses an approach which, for improving the crystallinity of a ferroelectric film of a stack-type capacitor structure, stacks an iridium film and an iridium oxide film to form the lower electrode. Thereafter, a first PZT film is formed, and a second PZT film thicker than the first PZT film is formed further.
Patent Document 3 discloses an approach which, for forming the ferroelectric film in which crystallization is facilitated at a low temperature of 650° C. or below, adds heteropoly acid to an organic metallic compound coating solution of SBT, PZT, or the like.
Patent Document 1: Japanese Patent Application Laid-open No. 2005-183841
Patent Document 2: Japanese Patent Application Laid-open No. 2003-68991
Patent Document 3: Japanese Patent Application Laid-open No. 2003-128419